Conditional Formatting on Button Block

Hello,

I am looking for some assitance on how I can assign the correct variable to make a "Continue" button route to a new slide after the slide has already been visited. 

In my course, I have disabled forward and back buttons via the TOC and have "Back" and "Contiune" buttons on each slide to enable a forced navigation through my course. 

The course consists of video content slides followed by review question slides. When the user visits the slide for the first time and presses "Continue" it will take them to the next review question slide. After they pass the review question they are then taken to the next video slide and so on.

My issues is that the users have a "Back" option on video slides so they can review previous content. The back buttons skip the recently passed review question and route back to the most recent video slide.

Ex:

Slide 1 = video

Slide 2 = review question 

Slide 3 = video 

etc....

When a user presses the "Back" button on slide 3, it takes them to slide 1 in case they would like to review content. When on Slide 1 again, and the user presses "Continue" on the second visit I would like the "Continue" button to skip past slide 2 and back to slide 3 again.

What would be the best way to set up a variable to adjust after the slide is visited again? 

Thanks for your help!